This invention relates to a pulverized coal burner capable of carrying out combustion in a stable state with a reduction in the amounts of NOx, CO and unburned carbon produced as the result of combustion.
A pulverized coal burner of the type shown in FIG. 1 is known as producing NOx in reduced amounts, which comprises a pulverized coal swirler 2 located within a primary throat 1 concentrically therewith at the forward end thereof, a secondary throat 3 located outside the primary throat 1 concentrically therewith, and a burner throat 4 located outside the secondary throat 3 concentrically therewith.
The pulverised coal burner of the aforesaid construction producing reduced amounts of NOx operates such that pulverized coal is carried by primary air through the primary throat 1 and swirled by the swirler 2 at the forward end of the primary throat 1 to pass in vortical flow, before being blown into a furnace. Meanwhile secondary air is ejected through the secondary throat 3 into the furnace without being swirled, and tertiary air is ejected through the burner throat 4 into the furnace without being swirled. The pulverized coal blown into the furnace after being caused to flow in vortical form by the swirler 2 is ignited and burns in the presence of the primary air and produces a primary flame 5. Unburned components of the pulverized coal burn in the presence of the secondary and tertiary air ejected through the secondary throat 3 and burner throat 4 respectively into the furnace, to form a secondary flame 6. The primary air, secondary air and tertiary air are distinct from one another in amount, and when their amounts are added together, the total is equal to the amount of air necessary for burning the pulverized coal in complete combustion. In practice, the primary air and pulverized coal are caused to pass in vortical flow by the swirler 2 so that they quickly mix with the secondary air and tertiary air and combustion takes place at once. Thus the amounts of NOx produced as the result of combustion show no marked reduction.
On the other hand, in a pulverized burner of the construction in which quick mixing of the primary air and pulverized coal with the secondary and tertiary air is avoided by reducing the speed at which the primary air and pulverized coal are swirled, a marked reduction could be obtained in the amounts of NOx produced but the flame formed in the furnace could not be sustained and stability of combustion would be lost, resulting in an increase in the amounts of CO and unburned carbon produced.